1. Field of the Invention
The present invention relates to a rotary encoder, and in particular, to a link structure of a rotary body (a recording medium) on which positional information is formed and a drive shaft driving a rotary motion of the rotary body.
2. Description of the Prior Art
The rotary encoder is used when a positional information pattern is recorded on a rotary body as a recording medium in various methods such as an electromagnetic method, an optical method, and a mechanical method and the rotary angle of the rotary body is detected by a magnetic sensor, an optical sensor, or a mechanical sensor depending on the kind of the positional information pattern. The rotary encoder has been broadly utilized in various fields in association with the recent development of the mechatronics.
When using the rotary encoder, the rotary body must be directly linked to a driving shaft such as a drum shaft or a motor shaft depending on the detection object (for example, a drum or a motor of a copying machine) of which the rotary angle is to be measured. However, it is quite difficult to continuously maintain the arrangement of the rotary axis of the rotating body and the driving shaft on the same axial line, namely, there appear a shift of center between the axes thereof (eccentricity) and a shift of inclination therebetween (declination) to some extent with respect to the center lines of the rotating shaft of the rotary body and the driving shaft due to an error in the installation thereof and an error in manufacturing the rotary body and the driving shaft. Consequently, in the prior art technology, the rotating axis of the rotary body is linked with the driving shaft, for example, by means of a universal joint called a helical coupling manufactured by forming a helical groove in a surface of a cylindrical body, thereby absorbing the eccentricity and the declination.
However, in the link structure of the prior art technology, since both ends of the helical coupling must be fixed on the rotary shaft of the rotary body extruding from the rotary encoder and on the driving shaft disposed on the apparatus side by means of suitable means such as screws, the installation thereof becomes complicated and a dedicated space is required for the installation thereof, which leads to a disadvantage to minimize the size of the apparatus. Furthermore, although the helical coupling develops a satisfactory effect with respect to the declination because of the inflection thereof, the allowance for the eccentricity is small. Particularly, since the amount of eccentricity is generally greater than that of the declination in this kind of link structure due to the clearance of the installing holes and the like, there may arise a disadvantage in some cases that the rotation force of the driving shaft cannot be imparted to the rotary body.